Solvent systems for polymeric dielectric materials

ABSTRACT

Aromatic aliphatic ether solvents, such as anisole, methylanisole, and phenetole, have been found useful in formulating coating solutions of polymeric dielectric materials and as a clean up solvent in the coating process. A process for forming a dielectric film on a substrate includes depositing a coating solution of a dielectric material in a formulation solvent onto a surface of the substrate and depositing an aromatic aliphatic ether solvent onto an edge portion of the surface of the substrate. The process is used to form films of dielectric materials including arylene ether dielectric polymers, hydridosiloxane resins, organohydridosiloxane resins, spin-on-glass materials, partially hydrolyzed and partially condensed alkoxysilane compositions which are cured to form a nanoporous dielectric silica material, and poly(perhydrido)silazanes.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/235,141 entitled “Solvent Systems for Low DielectricConstant Polymeric Materials,” filed Jan. 21, 1999, and U.S. Pat. No.6,291,628.

BACKGROUND

1. Field of the Invention

This application relates generally to dielectric materials including lowdielectric constant polymer materials and more particularly to solventsystems for use in formulation and clean up processing of suchmaterials.

2. Description of the Related Art

As the dimension of the interconnect design rules for integratedcircuits (IC) undergoes progressive shrinkage to sub-quarter micronmetal spacing, the use of polymer dielectrics that minimize capacitanceand reduce power consumption and cross talk, while increasing signalpropagation speed becomes a necessity. The dielectric materials mustpossess dielectric constants no higher than 3.0 and should havedielectric constants as low as possible toward a theoretical limit of1.0. The practical expectation for polymer dielectrics is in the rangeof 2.2 to 3.0. Both inorganic and organic polymer dielectrics arepotentially useful. For organic dielectrics, the glass transitiontemperature is an important consideration. The organic dielectrics musthave glass transition temperatures above 300° C. and as high as possibletoward 450° C., a value determined by the thermal stability of organicpolymers. The organic dielectrics should also be easily processed,preferably, by standard spin-bake-cure processing techniques. Theorganic dielectrics should also be free from moisture and out-gassingproblems, in addition to having expected adhesive and gap-fillingqualities, and dimensional stability towards thermal cycling, etching,and chemical mechanical polishing processes.

Arylene ether polymers have been identified as organic dielectricmaterials. Arylene ether polymers include poly(arylene ethers) (PAE)such as the FLARE™ material of AlliedSignal Inc. and the VELOX™ materialof Schumacher. Other useful arylene ether polymers include poly(aryleneether ketone) (PAEEK), poly(arylene ether ether acetylene) (PAEEA),poly(arylene ether ether acetylene ether ether ketone) (PAEEAEEK),poly(arylene ether ether acetylene ketone) (PAEEAK), andpoly(naphthylene ether) (PNE) comprising different polymer designs thatinclude homopolymers, block or random copolymers, polymer blends,interpenetrating polymer networks (IPNs), and semi-interpenetratingpolymer networks (SIPN)s. Additional examples of organic dielectricmaterials in current use include the polymeric material obtained fromthe phenyl-ethynylated aromatic monomer provided by the Dow ChemicalCompany under the tradename SiLK™.

Organosilicon polymers have also been identified as low dielectricconstant materials. In particular, siloxane based resins includinghydridosiloxane resins, organohydridosiloxane resins, and spin-on-glasssiloxanes and silsesquioxanes are used as dielectric layers. Otherclasses of organosilicon materials include poly(perhydrido)silazanes andnanoporous dielectric silica coatings formed from liquid alkoxysilanecompositions.

Taking advantage of the low dielectric property of organic-containingpolymeric materials requires the IC industry to continue to shift itsprocessing paradigm. Processing approaches, such as the use ofspin-coating, require selection of appropriate solvents for formulationof the coating solution, and for cleaning, edge-bead removal, and waferbackside rinsing. Desirable formulations will provide spin-coatedpolymer dielectric films with excellent uniformity, a wide thicknessrange from hundreds of angstroms to hundreds of microns, very lowout-gassing at high temperature, excellent gap-filling to 0.1 micron,excellent local, regional and global planarization, and ease of waferedge bead removal and wafer backside rinsing. In addition, thedielectric polymer solution should be easily filtered to minimize itsmanufacturing cost.

While conventional alcoholic solvents, familiar to IC engineers, areobvious solvent candidates, they cannot necessarily be applied toorganic materials. Ketonyl and other aprotic solvents have been used forphotoresists and polymer dielectrics. In particular, cyclic ketonylsolvents are commonly used as solvents for arylene ether dielectrics.However, cyclic ketones normally are not as miscible with most aryleneether polymer dielectrics as would be desired and the spin-on solutionsformulated from these solvents usually yield some extent of striation onthe spin-coated film, especially for films with thicknesses greater than1.5 micron. Serious striation could cause inadequate gap-filling,problems in adhesion of the dielectric film with a substrate and otherproblems. Additionally, cyclic ketonyl solvents have varying degrees ofmoisture, pH, and photosensitivities, often exacerbated by heat. Forexample, cyclopentanone is significantly more sensitive than firstthought toward low pH, in addition to its well-known sensitivity towardlight, moisture, and high pH. Cyclohexanone is more stable thancyclopentanone and has been a fair solvent for photoresists in theindustry. However, cyclohexanone is still sensitive to light andnon-neutral pH.

In addition, the solvents used must be environmentally acceptable.Cyclohexanone, discussed above, is considered to be barely tolerable bythe industry due to its very low exposure limit. Given that 80% of allsolvent used for spin-on processes, for example, is used at the clean upstage, including edge bead removal, wafer backside rinsing andspin-coater cup and nozzle rinsing, it is particularly important thatthe clean up solvent satisfy environmental considerations. It has alsobeen recognized that solvents preferably should have sufficiently highflash points. For example, the inorganic spin-on polymer ofpoly(perhydrido)silazane is conventionally formulated in dibutyl ether,a solvent with a flash point of only 25° C. Increasingly stringentenvironmental requirements place new constraints on solvents used withall of the dielectric materials, organic, organosilicon, and inorganicpolymers alike.

As knowledge in the application and processing of dielectric materialsexpands, shortcomings among the currently-used solvents are becomingmore recognized. It would be desirable to provide process compatible andbenign solvents for a wide range of dielectric polymer materials used inthe semiconductor industry. In particular, it would be desirable toprovide a family of extremely useful high-boiling point solvents forformulation of dielectric polymer solutions, edge bead removal of thesedielectric films, and process equipment rinsing.

SUMMARY

In accordance with this invention, there is provided a new family ofhigh boiling point, high flash point solvents, namely aromatic aliphaticethers, which are utilized in the formation of dielectric polymersolutions and as a clean up solvent in the deposition of such materials.The chemical structures of this family of ethers is presented below.Several significant examples of this family are anisole (C₆H₅OCH₃, n=1,m=0) and phenetole (C₆H₅OC₂H₅, n=2, m=0) with a boiling point of 155 and170° C., respectively, and 2-, 3-, or 4-methylanisole with a boilingpoint in the range of 170° C. to 175° C. The flash points of anisole andphenetole are 52° C. and 63° C., respectively.

Solvent R R₁ to R₅

C_(n)H_(2n+1) n = 1 to 6 C_(m)H_(2m+1) m = 0 to 3

A process for forming a dielectric film on a substrate includesdepositing a coating solution of a dielectric material in a formulationsolvent onto a surface of the substrate and depositing an aromaticaliphatic ether solvent onto an edge portion of the surface of thesubstrate. Depositing the aromatic aliphatic ether solvent on the edgeportion of the substrate surface provides edge bead removal. In theprocess of depositing these materials, the aromatic aliphatic ethers arealso advantageously used for the clean up processes of wafer backsiderinsing and equipment rinsing, such as spin-coater cup and nozzlerinsing.

The aromatic aliphatic ether solvent family is used as a clean upsolvent in depositing a wide variety of dielectric materials. Mixturesof one or more of these solvents may be employed in this invention. Thematerials include organic polymers, particularly arylene etherdielectric polymers including poly(arylene ether) (PAE), poly(aryleneether ether ketone) (PAEEK), poly(arylene ether ether acetylene)(PAEEA), poly(arylene ether ether acetylene ether ether ketone)(PAEEAEEK), poly(arylene ether ether acetylene ketone) (PAEEAK) andtheir block or random copolymers and blends, including their blends withpoly(carbosilanes). Organic dielectric materials also include porouspoly(arylene ethers) and polymeric materials obtained from coatingsolutions of phenyl-ethynylated aromatic monomers.

The aromatic aliphatic ethers are also used as clean up solvents in thedeposition of organosilicon dielectric materials. These materialsinclude porous and non-porous films of hydridosiloxane resins,organohydridosiloxane resins, and spin-on-glass materials such asmethylsiloxanes, methylsilsesquioxanes, phenylsiloxanes, andphenylsilsesquioxanes. They further include partially condensedalkoxysilane compositions which are cured to form a nanoporousdielectric silica material, and poly(perhydrido)silazanes.

According to another embodiment of the present invention, a process forproducing low dielectric films on semiconductor substrates uses acoating solution of a dielectric material formulated in an aromaticaliphatic ether solvent. The process is used to apply dielectricmaterials including arylene ether dielectric polymers and polys. Filmsproduced by this process advantageously have high thickness uniformityand do not exhibit striation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1 b are measured edge profiles of a 1 μm thick layer ofFLARE™ where edge bead removal was performed with anisole using a 5second and 1 second dispense time, respectively, according to an aspectof the present invention.

FIG. 1c is the measured edge profile of the same material where edgebead removal was performed with cyclohexanone using a 5 second dispensetime, according to the prior art.

DETAILED DESCRIPTION

Aromatic aliphatic ether solvents, such as anisole, methylanisole, andphenetole, have been found useful in formulating coating solutions ofspin-on dielectric materials and as a clean up solvent for the processesof edge bead removal, wafer backside rinsing, and equipment rinsing.

The aromatic aliphatic ethers have the general formula

where R is C_(n)H_(2n+1), n=1 to 6 and R₁ to R₅ is C_(m)H_(2m−1), m=0 to3. Advantageous examples of aromatic aliphatic ethers include anisole,C₆H₅OCH₃, where R=CH₃, corresponding to n=1 and R₁ to R₅=H,corresponding to m=0, and phenetole, C₆H₅OC₂H₅ where R=C₂H₅ (n=2) and R₁to R₅=H (m=0). The boiling points of anisole and phenetole are 155° C.and 170° C., respectively. Other advantageous solvents include 2-, 3-,and 4-methylanisole with a boiling point in the range of 170° C. to 175°C.

In particular, the aromatic aliphatic ether solvents have been founduseful for formulation and clean up of arylene ether polymers. Anexample of such a polymer is FLARE™ poly(arylene ether) of AlliedSignalInc. These polymers have flexible structural moieties built into theuncured structures thereby maintaining the polymers' flexibility and lowmelt viscosity, which allows them to be formulated for spin-coating.After being spun onto the surface of a wafer, the polymers are thermallyactivated to undergo a cross-linking reaction and cured to give rise toa T_(g) value above 250° C. and typically in the range of 300° C. to450° C., without additional assistance from cross-linking additives.

The chemical structures shown below are two examples of poly(aryleneethers) which may be used as dielectric materials in the IC industry.The dielectric constant for arylene ether polymers typically fallsbetween 2.5 to 3.0, which meets the requirement of next generationdielectrics for ultra large scale integration (ULSI).

In formula 2 above, y is between 0 and 1. In both formulas 2 and 3, x istypically between about 2 and about 200. Preferably, x is between about2 and about 100.

The polymer represented by formula 2 is disclosed, for example, in U.S.patent application Ser. No. 08/990,157 filed Dec. 12, 1997, to Lau etal. entitled “Poly(arylene ether) Compositions and Methods ofManufacture Thereof,” which is commonly assigned with the presentapplication and incorporated herein by reference.

Another example of a material useful in forming organic dielectric filmsis the end-capped poly(arylene ether) homopolymer of the general formula

where z is between 1 and about 200, Y and Ar are each a divalent aryleneradical and Z is a methyl group or a monovalent aryl radical. Polymersof formula 4 are disclosed in U.S. patent application Ser. No.09/197,478 to Lau et al. entitled “Poly(arylene ether) HomopolymerCompositions and Methods of Manufacture Thereof,” which is commonlyassigned with the present application and incorporated herein byreference.

In addition to finding application with the poly(arylene ether) polymersof formulas 2 to 4 above, the aromatic aliphatic ethers areappropriately used as solvents with organic dielectric polymersincluding poly(arylene ether ether ketone) (PAEEK), poly(arylene etherether acetylene) (PAEEA), poly(arylene ether ether acetylene ether etherketone) (PAEEAEEK), poly(arylene ether ether acetylene ketone) (PAEEAK)and their block or random copolymers and blends. Mixtures of one or moreof these solvents may be employed in this invention. Alternatively, asolvent mixture including one or more aromatic aliphatic ether solventsand cyclohexanone may be used.

Polymer solutions, in accordance with embodiments of the presentinvention, are formed by combining aromatic aliphatic ethers and lowdielectric constant polymers, such as arylene ether polymers, underambient conditions in any conventional apparatus having a non-metalliclining. Preferably, a glass-lined apparatus is employed. The resultingsolution is comprised of, based upon the total weight of the solution,from about 1 to about 50%, and preferably from about 5% to about 30% ofthe polymer dielectric and from about 50% to about 99%, and preferablyfrom about 70% to about 95% of solvent.

The resulting solution is then filtered under ambient conditions via anyof the filtration devices well known in the art including, but notlimited to commercially available filtration cartridges having thedesired porosity. It is generally preferable to use a filtration devicehaving a pore size less than about 1.0 μm. A typical filtration uses apore size of about 0.1 μm. Alternatively, the solution is filteredsequentially through about 4 filtration means of decreasing pore size,the final pore size being approximately 0.1 μm or less.

Typically, the solutions are applied to semiconductor wafers using aspin-coating process. However, dip-coating, spray-coating, or othercoating methods known in the art, can also be employed. The followingdescription of a spin-coating process is generally applicable to thewide range of polymeric dielectric materials used in the semiconductorindustry. In the spin-coating process, the polymer solution is dispensedonto a silicon wafer substrate at or near its center. In someembodiments, the wafer will remain stationary during the dispense cycle,while in some embodiments, the wafer will turn or spin at a relativelylow speed, typically less than about 1000 revolutions per minute (rpm).The dispense cycle is optionally followed by a short rest period andthen additional spins, hereinafter referred to as thickness spins,generally between approximately 2000 and 5000 rpm, although other spinspeeds may be used, as appropriate. In one typical process, the dispensestep includes a 5 second spin at 1000 rpm while the solution isdispensed and a subsequent 1 second spreading spin at 1000 rpm. Thedispense step is followed by a 30 second thickness spin at 2000 rpm. Thecoating process additionally includes cleaning steps discussed in moredetail below

Once the coating process is completed, the coated substrate, that is thesubstrate coated with the polymer solution, is heated to effect a bakeprocess and a subsequent cure process. Any conventional apparatus knownin the art can be employed for these processes. Preferably, theapparatus for the bake process is an integral part of a spin-coatingapparatus used for coating the substrate or wafer, although a separateapparatus for curing coatings is also suitable. The bake process can becarried out in an inert atmosphere such as an atmosphere of an inert gasor nitrogen. One commonly employed heating apparatus employs one or more“hot plates” to heat the coated wafer from below. The coated wafer istypically heated for up to about 120 sec at each of several hot platesat successively higher temperatures. Typically, the hot plates are attemperatures between about 70° C. and 350° C. One typical processemploys a heating apparatus having three hot plates. First, the wafer isbaked for about 60 sec at 150° C. Then the wafer is transferred to asecond hot plate for an approximately 60 sec bake period at 200° C.Finally, the wafer is transferred to a third hot plate for a third bakeperiod of approximately 60 sec at 250° C.

A final cure process is often employed to complete the curing of thefilm. The cure is preferably performed in an inert atmosphere, asdescribed above for the bake. This final cure process can employ aconventional thermal curing apparatus, for example a horizontal furnacewith a temperature range of about 300° C. to about 450° C. andpreferably from about 375° C. to about 425° C. In one typical furnacecure process, the baked wafer is cured for 30 minutes to one hour at400° C. at a nitrogen flow rate of 4 liters/min to 20 liters/min.

It will be understood that the above bake and cure processes weredescribed for illustrative purposes only and that other temperatures,durations, and number of bake cycles can be employed, where appropriate.

It has been found that solutions of arylene ether polymers such as thoseof formulas 2 and 3, formulated in anisole, methylanisole, and phenetoleyield totally striation-free films. In contrast, as demonstrated inExample 3 below, films produced from solutions in conventional solventsexhibit striation. Owing to the better polymer solubility, the workablespin speed range in the spinning step is wider than the correspondingcyclohexanone solutions. The standard deviation of uniformity of filmspin-coated from anisole, methylanisole, or phenetole solutions over thesilicon wafers is found to be lower than that of films spin-coated fromthe corresponding cyclohexanone solution. For example, the standarddeviation of a film formed from an 18 weight % solution of a polymer offormula 2 in phenetole was less than 0.3%. Additionally, the lowerviscosity of the anisole, methylanisole, and phenetole solutions permitthe polymer dielectric solution to be still effective at filling narrow(<0.15 μm), high aspect ratio gaps at high spin speed, such as in the4000 to 5000 rpm range. The wider window of these solutions yields awider thickness range for each version of spin-on polymer solution thanthe corresponding cyclohexanone solution.

In the coating process described above, the coating solution istypically dispensed on a spinning wafer substrate. The force exerted onthe spinning coating solution may cause an amount of the solution tobuild up on the edge portion of the substrate forming an edge bead.Typically the edge bead is displaced about 3 mm from the edge of thewafer. The coating process additionally includes the process of edgebead removal which is performed after dispensing the coating solutionand before the coated substrate is baked and cured. The edge beadremoval process includes dispensing a solvent from a nozzle positionednear the edge of the wafer such that the solvent is deposited on an edgeportion of the surface of the substrate including the edge bead. Atypical process includes a from 1 to 5 second dispense spin at 1500 rpmand a spin dry step consisting of a 2 to 6 second spin at from 1500 to3000 rpm.

Following the coating solution deposition and proceeding the edge beadremoval, additional cleaning steps are typically carried out. Thesecleaning steps, for which some typical parameters are provided, includea wafer backside rinse (5 second spin at 800 rpm), and a nozzle rinse (1second spin at 3000 rpm). The aromatic aliphatic ethers areadvantageously used as solvents for the wafer backside rinsing, edgebead removal, and general equipment clean up because of the highermiscibility of poly(arylene ether) polymers in aromatic aliphatic ethersthan in conventional solvents. In particular, as shown in Example 5below, when anisole is used for edge bead removal of a solution ofpolymer 2, considerably less solvent is needed than when cyclohexanoneis used. For a 200 mm wafer, a 1 sec dispense time which uses only 1 mlof anisole is sufficient while for cyclohexanone a 5 sec dispense timewhich requires five times as much solvent is typically used. Thus,anisole has been demonstrated to be effective for both formulation andclean up of poly(arylene ether) films, where clean up, as used here,includes edge bead removal, wafer backside rinsing, and coater equipmentrinsing. Use of the same solvent used throughout the spin coatingprovides an additional environmental advantages due to the ease ofrecycling.

As discussed above, the aromatic aliphatic ether solvents presented hereare useful as clean up solvents for use with a variety of organicpolymer dielectric materials. These include not only the arylene etherpolymers listed above and porous films of arylene ether polymers, butalso organic dielectrics such as the polymeric material obtained fromthe phenyl-ethynylated aromatic monomers and oligomers provided by theDow Chemical Company under the tradename SiLK™ and poly(arylene ether)provided by Schumacher under the tradename VELOX™. Additionally, thearomatic aliphatic ether solvents are used as clean up solvents forpoly(arylene ethers) blended with poly(carbosilanes). Furthermore,although the spin-coating technique has been presented in detail, thesolvents according to the present invention, can be used as clean upsolvents for edge bead removal and equipment rinsing for other coatingtechniques, such as those that do not involve a spin step.

A second class of dielectric materials with which aromatic aliphaticether solvents are used is materials containing siloxane resins.Examples of such resins are the organohydridosiloxane resins having oneof the four general formulas:

 (HSiO_(1.5))_(n)(RSiO_(1.5))_(m);  5

(H_(0.4-1.0)SiO_(1.5-1.8))_(n)(R_(0.4-1.0)SiO_(1.5-1.8))_(m);  6

(H_(0-1.0)SiO_(1.5-2.0))_(n)(RSiO_(1.5))_(m);  7

or

(HSiO_(1.5))_(x)(RSiO_(1.5))_(y)(SiO₂)_(z)  8

where the sum of n and m is from about 8 to about 5000 and m is selectedsuch that the organic substituent is present in an amount from about 1mole percent (Mol %) to about 99 Mol %; the sum of x, y, and z is fromabout 8 to about 5000 and y is selected such that the organicsubstituent is present in an amount from about 1 Mol % to about 99 Mol %and R is selected from substituted and unsubstituted straight chain andbranched alkyl groups, cycloalkyl groups, substituted and unsubstitutedaryl groups, and mixtures, thereof. The specific mole percent of carboncontaining substituents is a function of the amounts of startingmaterials. Polymers of formula 5-8 are further described in U.S. patentapplication Ser. Nos. 09/044,798 and 09/044,831, which are commonlyassigned with the present application and incorporated herein byreference.

Dielectric films from organohydridosiloxane resins are typically formedby a spin-coating process that is substantially similar to the processdescribed above in connection with poly(arylene ether) films. Thedeposition for such resins is further described in U.S. patentapplication Ser. Nos. 09/227,035 and 09/227,498, which are commonlyassigned with the present application and incorporated herein byreference.

The coating process for organohydridosiloxane resin solutions typicallyalso includes an edge bead removal step after the spin deposition step.The aromatic aliphatic ethers are particularly effective at edge beadremoval of films of organohydridosiloxane resins. For example, usinganisole for edge bead removal of a methylhydridosiloxane resin with 80%methyl content produces a very good edge profile. As described inExample 6 below, for these materials, the process of edge bead removaltypically uses two dispense steps, each about a 3 second spin at about1000 rpm. The aromatic aliphatic ethers are similarly effective for theremainder of the clean up processes in preparing films oforganohydridosiloxane resins including wafer backside rinsing, andcoater equipment cleaning, such as spin-coater cup and nozzle rinsingand line flushing.

Another low dielectric constant organosilicon material is the nanoporoussilica dielectric coating formed from an alkoxysilane compositioncontaining an alkoxymonomer of the formula:

where at least 2 of the R groups are independently C₁ to C₄ alkoxygroups and the balance, if any, are independently selected from thegroup consisting of hydrogen, alkyl, phenyl, halogen and substitutedphenyl. Preferably, each R is methoxy, ethoxy, or propoxy. Such polymersare commercially available from AlliedSignal as Nanoglass™. The mostpreferred alkoxysilane monomer is tetraethoxysilane (TEOS).

The aromatic aliphatic ethers are also advantageously used in the cleanup phase of depositing the alkoxysilane materials. To form a nanoporoussilica coating, a partially hydrolyzed and partially condensedalkoxysilane composition including an alkoxysilane monomer of formula 9in a suitable solvent is spin deposited on a wafer substrate. The coatedsubstrate is subsequently cured, in a final step, to form a nanoporoussilica coating. Following deposition, edge bead removal of thealkoxysilane material is typically performed using the solventpropyleneglycol methylether acetate (PGMEA) according to a protocolwhich includes two dispense spins and two drying spins. During the firstdispense spin, a nozzle is positioned a first distance from the edge ofthe wafer, for example, between about 3 mm and 8 mm from the edge for a200 mm wafer, to partially remove the edge bead. During the seconddispense spin, the nozzle is positioned slightly further from the edge,to substantially remove the edge bead. The alkoxysilane compositiondeposition and edge bead removal process is detailed in U.S. patentapplication serial number 09/156,220 entitled “Edge Bead Removal forNanoporous Dielectric Silica Coatings,” which is commonly assigned withthe present application and incorporated herein by reference.

As described in Example 7, for the alkoxysilane material prepared fromthe TEOS monomer using PGMEA as the solvent, two dispense spins, thesecond of which is 5 seconds in length are used. For anisole as the edgebead removal solvent a single dispense spin of 0.5 seconds is sufficientfor good edge profiles. Thus use of anisole accomplishes edge beadremoval with only a tenth the volume of solvent. The aromatic aliphaticethers are similarly effective for other clean up processes in preparingporous films from alkoxysilane monomers including wafer backsiderinsing, spin-coater cup and nozzle rinsing and line flushing.

In addition, the solvents are used for clean up processes in preparingother porous films, in particular porous films of theorganohydridosiloxane resins of formulas 5-8. They are also used forclean up with coating solutions of spin-on-glass materials such asmethylsiloxanes, methylsilsesquioxanes, phenylsiloxanes andphenylsilsesquioxanes, including clean up for processes for porousspin-on-glass materials. With respect to deposition of these and all ofthe dielectric materials enumerated, the solvents according to thepresent invention, can be used as clean up solvents for edge beadremoval and equipment rinsing for coating techniques that do not involvea spin step.

In yet another application, the aromatic aliphatic ethers presented hereprovide advantageous solvent media for both formulation and clean up ofinorganic spin-on polymers, particularly the polymer ofpoly(perhydrido)silazane. The poly(perhydrido)silazane is typicallyformulated in dibutyl ether (DBE), a solvent with a flash point of only25° C. Poly(perhydrido)silazane is provided under the name ASP™ by theTonen Corporation. Because of the low flash point and for otherenvironmental reasons, DBE is not an industrially preferred solvent. Incontrast, anisole has a flash point of 52° C. and phenetole has a flashpoint of 63° C. Anisole is advantageously used as a formulation solventfor poly(perhydrido)silazane in place of DBE. A coating solution ofpoly(perhydrido)silazane in anisole is spin deposited according to theprocess described above for deposition of poly(arylene ether) films.Films produced from poly(perhydrido)silazane formulated in anisole havean excellent film appearance. A 20% by weight resin solution ofpoly(perhydrido)silazane in anisole gave a film thickness of 4300 Åunder the same conditions where a 20% resin solution in DBE provided afilm thickness of 3800 Å. A further comparison of solvent properties andfilm results is provided below in Example 8. Anisole has further beendemonstrated to be an effective solvent for edge bead removal ofpoly(perhydrido)silazane films. A single dispense spin of 4.5 secondswas sufficient for good quality edge profiles.

The aromatic aliphatic ethers used in this invention, such as anisole,methylanisole and phenetole, are very stable organic solvents uponexposure to air., strong acid, and base even at elevated temperatures.Unlike, for example, cyclic ketonyl solvents, no derivatives of anisole,methylanisole, and phenetole are detected by gas chromatography (GC)when they are kept in contact with an acidic medium, for example, asulfonic acid type resin, in air for days. This greatly minimizes theout-gassing of polymer dielectric films at temperature of about 400° C.and above. Isothermal thermogravimetric analysis (ITGA) at 425 and 450°C. demonstrates significantly less weight loss for the film spin-coatedfrom anisole or methylanisole or phenetole solutions compared with thatof films spin-coated from cyclohexanone solution.

Anisole, methylanisole, phenetole, and the other aromatic aliphaticsolvents are very benign solvents to the environment and the workplace.Anisole has long been used in the perfume industry and no significanthazardous concerns have ever been raised. High purity anisole,methylanisole, and phenetole with less than 50 ppb for all metals arewidely commercially available at competitive prices. Together with allthe property improvement on the dielectric film of arylene etherpolymers, anisole, methylanisole, phenetole and other aromatic aliphaticether solvents provide more robust polymer dielectric films for thesemiconductor and microelectronic industries.

As a result, polymer dielectric solutions based on aromatic aliphaticether solvents, such as anisole, methylanisole and phenetole are benign,provide decreased manufacturing cost for the spin-on dielectric polymer,provide the polymer solutions with the capability to achieve highthickness, wider windows and a wider thickness range, and providestriation-free polymer dielectric films with improved gap-fillingcapability, low out-gassing and high glass transition temperatures.Furthermore, aromatic aliphatic ether solvents provide clean up solventsthat are effective, environmentally friendly, and that can dramaticallyreduce the total volume of solvent needed.

The methods of using aromatic aliphatic ether solvents for formulationof polymer dielectric materials and clean up processing are furtherillustrated in the following examples.

EXAMPLE 1

An 18 weight % solution of the poly(arylene ether) of formula 2 withy=0.5, the FLARE™ material of AlliedSignal, was prepared by dissolvingan appropriate weight of the solid polymer in phenetole under ambientconditions in a glass lined reactor. The solution was filtered through aseries of four Teflon® filtration cartridges. The filtration cartridgeshave decreasing nominal pore sizes of 1.0, 0.5, 0.2, and 0.1 μm,respectively.

EXAMPLE 2

Approximately 3 ml of the filtered solution of Example 1 was processedonto the surface of a four inch silicon wafer using a spin coater andhot plate oven track, for example a Silicon Valley Group, Inc. (SVG)Model No. 8828 coater and SVG model No. 8840 oven track. After thesolution was dispensed, the wafer was spun at 500 rpm for 5 seconds,followed by a 5 second rest and a 60 second spin at various speedsbetween 1000 and 5000 rpm, as reported below. The coated wafer was bakedat 180° C. for one minute. The baked wafer was then cured in a nitrogenatmosphere in a furnace set initially at 200° C. followed by a ramp to400° C. at 5° C./minute and a ramp to 425° C. at 1.5° C./minute, held at425° C. for one hour, followed by a cool down to 100° C. Properties ofthe resulting films are given below in Table 1.

TABLE 1 Properties of Films from 18 wt % Solution in Phenetole as aFunction of Spin Speed 1000 1500 2000 3000 4000 5000 Property rpm rpmrpm rpm rpm rpm Gap fill <0.15 <0.15 <0.15 <0.15 <0.15 <0.15 μm μm μm μmμm μm Planarization   75%   80%   75%   70%   68%   65% Thickness* 1,801Å 1,449 Å 1,260 Å 1,033 Å — — Uniformity** 0.44% 0.18% 0.23% 0.27% —Striation*** None None None None — — *Thickness after cure **Standarddeviation of five measurements ***Determined by examination underoptical microscope

EXAMPLE 3

13 wt % solutions of FLARE™ in the various conventional solvents wereprepared and processed into films as described in Examples 1 and 2 abovefor comparison with a polymer solution in phenetole. Films were gradedon thickness uniformity, defined as standard deviation <0.3% and opticalquality, defined as absence of striation on examination under an opticalmicroscope.

TABLE 2 Film Quality as Function of Solvent Optical Solvent UniformityQuality Phenetole Pass Pass 1:1 cyclohexanone/γ-butyrolactone Fail Fail1:1 cyclohexanone/ Fail Fail N-methylpyrrolidinone 1:1N-methylpyrrolidinone/ Fail Fail γ-butyrolactone 4:1cyclohexanone/diphenyl ether Pass Fail Diglyme Fail FailN,N-dimethylacetamide Fail Fail

EXAMPLE 4

A poly(arylene ether) homopolymer of formula 4 in which Y, Ar, and Zare:

respectively was prepared and combined with anisole to form an 18 wt %solution. After 3 ml of the solution was dispensed, the wafer was spunat 500 rpm for 5 seconds, followed by a 5 second rest and a 60 secondspin at 2000 rpm. The wafer was cured at 425° C. for one hour. Filmthickness was 1.06 μm after curing.

EXAMPLE 5

A 1 μm thick film of FLARE™ material was deposited on a silicon nitridecoated wafer substrate using a SEMIX TR 8132-C spin coater using theprocess recipe described in Example 2. After deposition and before thebake and cure steps, edge bead removal (EBR) was performed with anisoleand with the comparative solvent cyclohexanone according to the recipegiven below in Table 3.

TABLE 3 Parameters for EBR Of FLARE ™ Films Step Anisole CyclohexanoneDispense 1 sec or 5 sec 5 sec 1500 rpm 1500 rpm Spin dry 3 sec 3 sec1500 rpm 1500 rpm

Edge bead profiles measured after the bake and cure with a Sloan DektakII profilometer are compared in FIGS. 1a-1 c, which show profiles for a5 second and 1 second dispense with anisole as the edge bead removalsolvent and for a 5 second dispense with cyclohexanone as the solvent,respectively. Good profiles were obtained in all cases, in particularwith a 1 second anisole dispense time, which amounts to 1 ml of anisole,a factor of five smaller volume than used with cyclohexanone as thesolvent.

EXAMPLE 6

A polymer solutions of an 80% methyl organohydridosiloxane resin wascoated on a substrate using a conventional spin coater. Edge beadremoval was performed with anisole and with the comparative aliphatichydrocarbon solvent NRD provided by Ashland Chemical Co. (CAS registry8052-41-3) according to the following parameters. Bake and cure steps asdescribed in U.S. application Ser. No. 09/227,498 were performed.

TABLE 4 EBR of 80% Methyl Organohydridosiloxane Films Step Anisole NRDDispense 1 3 sec 3 sec or 5 sec 1000 rpm 1000 rpm Dispense 2 3 sec 3 sec1000 rpm 1000 rpm

The EBR dispense nozzle was moved closer to the edge between the firstdispense step and the second dispense step. A good edge profile wasobserved with anisole as the EBR solvent, equivalent to the results withthe comparative solvent NRD.

EXAMPLE 7

Deposition of a partially hydrolyzed and partially condensedalkoxysilane composition for forming nanoporous dielectric coatingscontaining TEOS, triethyleneglycol monomethylether, water and nitricacid was performed on a commercial spin coater (Dai Nippon Screen D-Spin80A). After deposition, edge bead removal was performed with anisole andwith the comparative solvent propyleneglycol methylether acetate (PGMEA)according to the following parameters.

TABLE 5 Parameters for EBR of TEOS composition Step Anisole PGMEADispense 1 0.5 sec 1 sec 1500 rpm 500 rpm Dispense 2 none 4 sec 1500 rpmSpin dry 1 1 sec 1 sec 2000 rpm 2000 rpm Spin dry 2 10 sec 10 sec 500rpm 500 rpm

The coated substrate was aged and cured. A good edge profile wasobserved using a single 0.5 sec dispense time with, requiring a factorof 10 smaller volume of solvent than using the comparative solventPGMEA.

EXAMPLE 8

A solution of poly(perhydrido)silazane in pyridine, ASP™2.0 (TonenCorporation) was solvent exchanged with anisole and with the comparativesolvent dibutyl ether (DBE) to prepare 20 wt % resin coating solutions.3 ml of the solutions were spin coated onto 6 inch silicon wafersubstrates. The wafer were spun at 2000 rpm for 60 seconds. Edge beadremoval was performed with anisole and DBE. A single dispense spin of4.5 seconds at 2000 rpm was used. Excellent edge profiles were obtainedwith anisole and DBE. The coated substrates were baked for 3 minuteseach on hot plates at 150° C., 200° C., and 300° C. and cured at 400° C.for 60 minutes under an oxygen flow of 5 liters/min. As shown in thefollowing table, excellent film appearance was obtained with anisole asa formulation solvent.

TABLE 5 Formulation solvents and films for poly(perhydrido)silazaneAnisole (20 wt % resin) DBE (20 wt % resin) Boiling Point 154° C. 151°C. Density 0.88 g/cm³ 0.75 g/cm³ Viscosity 1.2 cP 0.8 cP Solubility OKOK Film Thickness 4300 Å 3800 Å Film Appearance Excellent Excellent

Although the invention has been described with reference to particularexamples, the description is only an example of the invention'sapplication and should not be taken as a limitation. Various adaptationsand combinations of features of the examples disclosed are within thescope of the invention as defined by the following claims.

We claim:
 1. A process for forming a dielectric film on a substratecomprising: depositing a coating solution on a surface of the substrate,the coating solution comprising a dielectric material and a formulationsolvent; and depositing an aromatic aliphatic ether solvent onto an edgeportion of the surface of the substrate.
 2. The process of claim 1wherein the aromatic aliphatic ether solvent is a solvent having theformula

wherein R=C_(n)H_(2n+1) and n=1 to 6, and wherein each of R₁ to R₅ isindependently C_(m)H_(2m−1), wherein m=0 to
 3. 3. The process of claim 1wherein the aromatic aliphatic ether solvent is a solvent selected fromthe group consisting of anisole, methylanisole, phenetole and mixturesthereof.
 4. The process of claim 1 wherein the dielectric material is apoly(arylene ether).
 5. The process of claim 4 wherein the formulationsolvent comprises an aromatic aliphatic ether.
 6. The process of claim 4wherein the poly(arylene ether) is selected from the group consisting ofa polymer of the formulas:

wherein, in formula 1, y=0-1, and in both formulas 1 and 2, x is about 2to about
 200. 7. The process of claim 6 wherein the formulation solventis an aromatic aliphatic ether.
 8. The process of claim 4 wherein thepoly(arylene ether) is selected from the group consisting of a polymerof the formula:

wherein, in formula 3, Y, Ar, and Z are

respectively, and z is between 1 and about
 200. 9. The process of claim8 wherein the formulation solvent is an aromatic aliphatic ether. 10.The process of claim 1 wherein the dielectric material is selected fromthe group consisting of poly(arylene ether) (PAE), poly(arylene etherether ketone) (PAEEK), poly(arylene ether ether acetylene) (PAEEA),poly(arylene ether ether acetylene ether ether ketone) (PAEEAEEK),poly(arylene ether ether acetylene ketone) (PAEEAK), poly(naphthenylether) (PNE), and phenyl-ethynylated aromatic monomers and oligomers.11. The process of claim 1 wherein the dielectric material is anorganohydridosiloxane resin having a general formula:(HSiO_(1.5))_(n)(RSiO_(1.5))_(m), or(H_(0.4-1.0)SiO_(1.5-1.8))_(n)(R_(0.4-1.0)SiO_(1.5-1.8))_(m), or(H_(0-1.0)SiO_(1.5-2.0))_(n)(RSiO_(1.5))_(m), or(HSiO_(1.5))_(x)(RSiO_(1.5))_(y)(SiO₂)_(z), wherein the sum of n and mis from about 8 to about 5000 and m is selected such that the organicsubstituent is present in an amount of from about 1 mole percent toabout 99 mole percent; the sum of x, y, and z is from about 8 to about5000 and y is selected such that the organic substituent is present inan amount of from about 1 mole percent to about 99 mole percent; and Ris selected from substituted and unsubstituted straight chain andbranched alkyl groups, cycloalkyl groups, substituted and unsubstitutedaryl groups, and mixtures, thereof.
 12. The process of claim 1 whereinthe dielectric material is a partially hydrolyzed and partiallycondensed alkoxysilane composition, and wherein the process furthercomprises curing the alkoxysilane composition to form a nanoporousdielectric silica coating.
 13. The process of claim 1 wherein thedielectric material is a spin-on-glass material.
 14. The process ofclaim 1 wherein the dielectric material is poly(perhydrido)silazane. 15.The process of claim 14 wherein the formulation solvent is an aromaticaliphatic ether.
 16. The process of claim 1 further comprising rinsingthe wafer backside using an aromatic aliphatic ether solvent.
 17. Theprocess of claim 1 further comprising rinsing parts of the coatingequipment using an aromatic aliphatic ether solvent.
 18. The process ofclaim 17 wherein the process is performed on a spin coater and whereinrinsing parts of the coating equipment comprises spin-coater cup rinsingand nozzle rinsing.
 19. A polymeric solution comprising an inorganicspin-on polymer dissolved in an aromatic aliphatic ether solvent. 20.The solution of claim 19 wherein the polymer ispoly(perhydrido)silazane.
 21. The solution of claim 19 wherein thesolvent is a solvent having the formula

wherein R=C_(n)H_(2n−1) and n=1 to 6, and wherein each of R₁ to R₅ isindependently C_(m)H_(2m+1), wherein m=0 to
 3. 22. The solution of claim19 wherein the solvent is selected from the group consisting of anisole,methylanisole, phenetole and mixtures thereof.
 23. A microelectronicdevice comprising a dielectric film formed on a substrate by the processcomprising: depositing a coating solution on a surface of the substrate,the coating solution comprising a dielectric material and a formulationsolvent; and depositing an aromatic aliphatic ether solvent onto an edgeportion of the surface of the substrate.